Specifying non-existing resolver results in StatusCodeException (404)

[zudov]

Steps to reproduce:

1. put - resolver: 42.0 in stack.yaml
2. run stack build

Output:

2015-06-27 13:45:47.528651: [debug] Downloading build plan from: https://raw.githubusercontent.com/fpco/lts-haskell/master/lts-42.0.yaml @(stack_A9qpSwIoAUk1jSor4vUA5i:Stack.BuildPlan src/Stack/BuildPlan.hs:464:13)
Downloading lts-42.0 build plan ...StatusCodeException (Status {statusCode = 404, statusMessage = "Not Found"}) [("Content-Security-Policy","default-src 'none'"),("X-XSS-Protection","1; mode=block"),("X-Frame-Options","deny"),("X-Content-Type-Options","nosniff"),("Strict-Transport-Security","max-age=31536000"),("Content-Length","9"),("Accept-Ranges","bytes"),("Date","Sat, 27 Jun 2015 13:46:13 GMT"),("Via","1.1 varnish"),("Connection","keep-alive"),("X-Served-By","cache-fra1224-FRA"),("X-Cache","MISS"),("X-Cache-Hits","0"),("Vary","Authorization,Accept-Encoding"),("Access-Control-Allow-Origin","*"),("Expires","Sat, 27 Jun 2015 13:51:13 GMT"),("Source-Age","0"),("X-Response-Body-Start","Not Found"),("X-Request-URL","GET https://raw.githubusercontent.com:443/fpco/lts-haskell/master/lts-42.0.yaml")] (CJ {expose = []})

I think it would be better if more user-friendly error message was displayed. Something like:

Non-existing resolver specified: lts-42.

Do we need such improvement?

[chrisdone]

That would be nice!

[zudov]

@chrisdone, I would like to hack on this.

The failure lies in Stack.BuildPlan.loadBuildPlan:

            $logDebug $ "Downloading build plan from: " <> url
            _ <- download req fp

I guess simply catching the exception and displaying error message would be good enough.
I've also been thinking about adding something like download404 :: _ -> _ -> _ (Maybe Bool) (need some better name) which returns Nothing on 404, but that might be an overkill.

[chrisdone]

It could return a Status?

[chrisdone]

Although catching the exception and throwing a build-plan-specific exception is fine.

[zudov]

@chrisdone Hmm. Having something like:

-- | Same as 'download' but catching StatusCodeException and returning 'Status'
downloadWithStatus :: _ -> _ -> _ (Either Status Bool)

might be useful not only for this case.